Field of the Invention
The invention lies in the semiconductor technology field. More specifically, the present invention relates to a semiconductor component having a small forward voltage and a high blocking ability, in which at least one drift path suitable for taking up voltage is formed in a semiconductor body between two mutually spaced-apart electrodes.
Power MOS field-effect transistors should inherently have, on the one hand, a predetermined minimum breakdown voltage, but on the other hand the highest possible conductance with regard to the area of a semiconductor body that is used for them ("silicon area"). However, the minimum breakdown voltage and the conductance are coupled with one another in the case of customary semiconductor components: high conductivity is only obtained by a high doping and/or a small thickness or drift path length, which leads, however, to a low breakdown voltage and hence to a low blocking ability. In other words, a relatively high breakdown voltage and at the same time a high conductance cannot be achieved with conventional semiconductor components. This also applies to other unipolar semiconductor components such as, for example, Schottky diodes (in this context, see B. J. Baliga: "Modern Power Devices", John Wiley & Sons, 1987, in particular Equation 6.60, FIG. 6.23 and also pages 421 ff. and 132 ff.).
In addition to the power MOSFET disclosed above, various possibilities have already been conceived of with the aim of avoiding the problem of the coupling of breakdown voltage and conductivity, so that each of these two properties can be optimized in favor of itself.
In the first instance, there are semiconductor components known as IGBTs (insulated gate bipolar transistors), which are also referred to as IGT (insulated gate transistor) or as COMFET (conductivity modulated FET). In the case of such a semiconductor component, the inherently weakly doped drift path, that is to say the "central region" which has to take up the reverse voltage, is flooded, in the case of forward-biasing, with an electron-hole plasma having a considerably higher conductivity than the weak doping of the central region (cf. B. J. Baliga, pages 350-53).
Moreover, U.S. Pat. No. 4,941,026 discloses a semiconductor component in which the electric charge contained in the drift path doping is compensated for, in the case of reverse-biasing, by charges from a gate arranged in a deep trench. In the case of such a structure, the charge in the drift path contributes to the build-up of the vertical field strength between the two electrodes only is a greatly reduced manner and, therefore, can be chosen to be considerably higher compared with customary semiconductor components. Thus, by way of example, it is possible to introduce up to twice the breakdown charge as doping in a drift path region between two trenches.
Finally, consideration has also already been given for a relatively longtime to so-called compensation components, in the case of which compensation of the drift path charge in the case of reverse-biasing of the semiconductor component is provided by means of regions arranged parallel to the drift path or zones having an opposite doping to the drift path doping (in this respect, see U.S. Pat. No. 4,754,310 and U.S. Pat. No. 5,216,275). However, in the case of those prior art semiconductor components, too, the doping of the individual regions must not exceed twice the breakdown charge (2.times.10.sup.12 charge carriers cm.sup.-2 in the case of Si).
These so-called compensation components are based on mutual compensation of the charge of n- and p-doped regions in the drift path of a MOS transistor, for example. In this case, these regions are spatially arranged such that the line integral against the doping remains below the material-specific breakdown charge specified above, in other words below approximately 2.times.10.sup.12 cm.sup.-2 in the case of silicon. By way of example, in a vertical transistor of the kind that is customary in power electronics, p- and n-type "pillars" or "plates", etc. may be arranged in pairs. In a lateral structure, p- and n-conducting layers may be stacked alternately one above the other laterally between a trench occupied by a p-conducting layer and a trench occupied by an n-conducting layer (cf. U.S. Pat. No. 4,754,310).
The aforementioned compensation components require relatively accurate setting of the dopant concentrations in the individual zones and regions in order to actually achieve the desired compensation. This setting of the dopant concentrations has proved to be relatively difficult if, in particular, doping is intended to be performed over a relatively long period of time on different semiconductor chips.